RECOVERY OF POTASH IN THE CEMENT INDUSTRY. 33 
effective. The presence of sulphur dioxide in the furnace when the 
ignitions were made was found to have a retarding effect on the 
evolution of the potash. 
Since potash occurs in the form of feldspar or other silicates in the 
raw materials used in cement manufacture, it might be inferred from 
the experiments made on the ignition of feldspar mixtures and of 
cement materials that more or less complete volatilization of the 
potash would take place in the burning of cement. 
It happens, however, that the clinkering zone of a-rotary kiln 
constitutes only a comparatively short portion of its length, and 
while the time taken for the charge to pass through the kiln may 
vary from about 14 to 24 hours, depending on the length of the kiln, 
the time that the charge is subjected to a clinkering temperature 
does not exceed one-half hour. The length of a rotary kiln must 
- also act disadvantageously on the escape of the potash. That some 
potash is volatilized in cement burning has long been known, and 
in the case of one plant a quantitative study of the amount lost in 
this way has been made by R. K. Meade! from analyses of the raw 
material fed into the kiln, the resulting clinker, and the coal used 
for burning. The results of three separate tests showed that the 
potash volatilized ranged from 46 to 52 per cent. 
POTASH IN RAW MATERIALS AND LOSS THROUGH VOLATILIZATION 
IN CEMENT MANUFACTURE, 
With a view to securing more extended information in this direc- 
tion, an investigation was undertaken about five years ago to 
ascertain the percentage of potash occurring in the raw materials 
used in the different cement plants of this country and also the per- 
centage of the total potash that is volatilized in each case. Repre- 
sentative samples of raw mix and ground clinker were collected from 
the different cement plants in the United States and in Canada, with 
a view to analyzing each sample for potash. With the data thus 
obtained, and knowing the ratio between the raw mix and the cement 
produced, and the output of the latter, it was thought possible to 
calculate for each plant the approximate quantity of potash that 
escapes daily from the kilns. After the work was partly completed it 
had to be abandoned for a time. A few months ago the problem 
was taken up again and entirely new samples were collected. The 
work now has been completed, with the results given in Table I. 
This table shows that the potash occurring in the raw mix used by 
the different cement plants in this country varies from 0.20 to 1.16 
per cent. The raw materials used in the mills of the Universal Port- 
land Cement Co. consisting of blast-furnace slag and a high-grade 
limestone contain considerably less potash than the average for 
the other cement plants of the country. 
1 Chem. Engineer, 2, 221 (1905). 
